Antigen-induced breakdown of membrane phospholipids appeared to be mediated by Gz-like protein and a tyrosine kinase, the latter enzyme was possibly regulated by a phosphatase in basophilic RBL-2H3 cells. Other stimulants, for example, adenosine analogs or carbachol, in RBL-2H3 cells transfected with the gene for the muscarinic ml receptors, operate exclusively through G-proteins to activate phospholipase C and other phospholipases. The ensuing events, however, such as mobilization of intra- and extra- cellular Ca2+, activation of protein kinase C and exocytosis appear to be identical for all stimulants. In particular, all stimulants recruit Ca2+ from the same intracellular pool of Ca2+ and utilize the same Ca2+-influx mechanism. Studies with a variety of kinase and phospholipase inhibitors revealed that few were specific in action; many of them inhibited the tyrosine phosphorylation of phospholipase C and as a consequence of hydrolysis of inositol phospholipids and secretion.